U.S. patent application number 15/436322 was filed with the patent office on 2017-08-24 for rotor assembly of an electric motor.
The applicant listed for this patent is Moog Inc.. Invention is credited to Ping Peter Zhong.
Application Number | 20170244292 15/436322 |
Document ID | / |
Family ID | 58191688 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170244292 |
Kind Code |
A1 |
Zhong; Ping Peter |
August 24, 2017 |
ROTOR ASSEMBLY OF AN ELECTRIC MOTOR
Abstract
A rotor assembly of an electric motor generally comprises a
center shaft configured to rotate about a longitudinal axis and a
plurality of spacers extending radially outward from the center
shaft, the spacers fixedly attached to the center shaft. A
plurality of axially stacked annular laminations are coaxially
aligned with the center shaft and radially supported on an inner
circumferential surface by the plurality of spacers. Each of the
plurality of spacers has, at each axial end of the stacked annular
laminations, first and second axial restraining elements extending
in an outward radial direction beyond the inner circumferential
surface of the plurality of stacked annular laminations. The
plurality of stacked annular laminations are compressed between the
first axial restraining element and the second axial restraining
element, such that an axial compression force is applied to the
plurality of stacked laminations.
Inventors: |
Zhong; Ping Peter; (Amherst,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Moog Inc. |
East Aurora |
NY |
US |
|
|
Family ID: |
58191688 |
Appl. No.: |
15/436322 |
Filed: |
February 17, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62297714 |
Feb 19, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 1/30 20130101; H02K
1/278 20130101; H02K 7/003 20130101; H02K 15/03 20130101; H02K
1/2706 20130101; H02K 15/02 20130101 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 15/03 20060101 H02K015/03 |
Claims
1. A rotor assembly of an electric motor comprising: a center shaft
having a first end and an opposing second end, said center shaft
configured to rotate about a longitudinal axis; a plurality of
spacers extending radially outward from said center shaft; each of
said plurality of spacers fixedly attached to said center shaft
along an axially extending proximal edge of said spacer; an axially
extending distal edge of at least one of said plurality of spacers
having an axially extending first coupling element; a plurality of
axially stacked annular laminations coaxially aligned with said
center shaft and radially supported by said plurality of spacers;
each of said plurality of stacked annular laminations having a
second coupling element formed within an inner circumferential
surface of said lamination; and said first coupling element of said
spacer configured to mechanically engage said second coupling
element of said stacked annular laminations, wherein rotational
movement of said plurality of stacked annular laminations about
said longitudinal axis relative to said center shaft is
restrained.
2. The rotor assembly of an electric motor of claim 1, wherein said
plurality of spacers comprise axially elongated radial spokes
welded to said center shaft.
3. The rotor assembly of an electric motor of claim 1, wherein said
plurality of spacers and said center shaft form a single unitary
structure.
4. The rotor assembly of an electric motor of claim 1, wherein said
plurality of spacers are circumferentially spaced symmetrically
around said center shaft.
5. The rotor assembly of an electric motor of claim 1, wherein said
first coupling element comprises an axially elongated protrusion or
groove, and wherein said second coupling element comprises the
other of a protrusion or a groove configured to mate with said
first coupling element.
6. The rotor assembly of an electric motor of claim 1, wherein said
distal edge of at least two of said plurality of spacers each
having said axially extending first coupling portion, and wherein
each of said plurality of stacked annular laminations having a
plurality of second coupling portions configured to engage with
said at least two first coupling portions.
7. The rotor assembly of an electric motor of claim 1, wherein said
stacked annular laminations are in direct contact with said
spacers.
8. The rotor assembly of an electric motor of claim 1, wherein said
stacked annular laminations are shrink fit to said spacers.
9. The rotor assembly of an electric motor of claim 8, wherein said
stacked annular laminations are configured such that an inward
radial compression force is applied against said spacers.
10. The rotor assembly of an electric motor of claim 9, wherein
each of said stacked annular laminations are joined together by
said compression force, and wherein an external bonding agent is
not used to join together each of said stacked annular
laminations.
11. The rotor assembly of an electric motor of claim 1, further
comprising: each of said plurality of spacers having, on said
distal edge and at a first end of said stacked annular laminations,
a first axial restraining element extending in an outward radial
direction beyond said inner circumferential surface of said
plurality of stacked annular laminations; and a first annular end
plate coaxially aligned with said center shaft and positioned
axially between a first end annular lamination of said stacked
annular laminations and said first axial restraining element.
12. The rotor assembly of an electric motor of claim 11, further
comprising: each of said plurality of spacers having, on said
distal edge and at a second end of said stacked annular
laminations, a second axial restraining element extending in an
outward radial direction beyond said inner circumferential surface
of said stacked annular laminations; and a second annular end plate
coaxially aligned with said center shaft and positioned axially
between a second end annular lamination of said stacked annular
laminations and said second axial restraining element; and said
plurality of stacked annular laminations compressed between said
first annular end plate and said second annular end plate, such
that an axial compression force is applied to said plurality of
stacked laminations.
13. The rotor assembly of an electric motor of claim 11, wherein
said first axial restraining element comprises: a transversely
extending recess having a recess entrance in said distal edge of at
least one of said spacers; and a restraining key partially
supported in said recess and extending in an outward radial
direction beyond said recess entrance and said inner
circumferential surface of said stacked annular laminations.
14. The rotor assembly of an electric motor of claim 13, wherein
said restraining key has a length and a thickness that varies with
said length such that said axial compression force of said
plurality of stacked laminations can be selectively varied as a
function of said length of said restraining key supported in said
recess.
15. The rotor assembly of an electric motor of claim 12, wherein
said second axial restraining element comprises a restraining tab
extending from at least one of said spacers in an outward radial
direction beyond said inner circumferential surface of said stacked
annular laminations.
16. The rotor assembly of an electric motor of claim 1, further
comprising: a plurality of axially extending segmented magnets
attached to an outer surface of said stacked annular
laminations.
17. The rotor assembly of an electric motor of claim 16, further
comprising: said plurality of segmented magnets secured to said
outer surface of said plurality of stacked annular laminations by
an outer flexible band wrapped circumferentially around said
segmented magnets.
18. A rotor assembly of an electric motor comprising: a center
shaft configured to rotate about a longitudinal axis; a plurality
of spacers extending radially outward from said center shaft; each
of said plurality of spacers fixedly attached to said center shaft
along an axially extending proximal edge of said spacer; a
plurality of axially stacked annular laminations coaxially aligned
with said center shaft and radially supported on an inner
circumferential surface by said plurality of spacers: each of said
plurality of spacers having at a first axial end of said stacked
annular laminations a first axial restraining element extending in
an outward radial direction beyond said inner circumferential
surface of said plurality of stacked annular laminations; and each
of said plurality of spacers having at a second axial end of said
stacked annular laminations a second axial restraining element
extending in an outward radial direction beyond said inner
circumferential surface of said stacked annular laminations; and
said plurality of stacked annular laminations compressed between
said first axial restraining element and said second axial
restraining element, such that an axial compression force is
applied to said plurality of stacked laminations.
19. The rotor assembly of an electric motor of claim 18, further
comprising a first annular end plate coaxially aligned with said
center shaft and positioned axially between a first end annular
lamination of said stacked annular laminations and said first axial
restraining element and a second annular end plate coaxially
aligned with said center shaft and positioned axially between a
second end annular lamination of said stacked annular laminations
and said second axial restraining element, said plurality of
stacked annular laminations compressed between said first annular
end plate and said second annular end plate, such that an axial
compression force is applied to said plurality of stacked
laminations.
20. The rotor assembly of an electric motor of claim 18, wherein
each of said stacked annular laminations are joined together by
said axial compression force, and wherein an external bonding agent
is not used to join together each of said stacked annular
laminations.
21. The rotor assembly of an electric motor of claim 18, wherein
said first axial restraining element comprises: a transversely
extending recess having a recess entrance in said distal edge of at
least one of said spacers; and a restraining key partially
supported in said recess and extending in an outward radial
direction beyond said recess entrance and said inner
circumferential surface of said stacked annular laminations.
22. The rotor assembly of an electric motor of claim 21, wherein
said restraining key has a length and a thickness that varies with
said length such that said axial compression force of said
plurality of stacked laminations can be selectively varied as a
function of said length of said restraining key extending into said
recess.
23. The rotor assembly of an electric motor of claim 18, wherein
said second axial restraining element comprises a restraining tab
extending from at least one of said spacers in an outward radial
direction beyond said inner circumferential surface of said stacked
annular laminations.
24. The rotor assembly of an electric motor of claim 18, further
comprising: said distal edge of at least one of said plurality of
spacers having an axially extending first coupling element; each of
said plurality of stacked annular laminations having a second
coupling element formed within said inner circumferential surface
of said lamination; and said first coupling element of said spacer
configured to mechanically engage said second coupling element of
said stacked annular laminations, wherein rotational movement of
said plurality of stacked annual laminations about said
longitudinal axis relative to said center shaft is restrained.
25. The rotor assembly of an electric motor of claim 18, further
comprising: said spacers welded to said center shaft such that said
spacers and said center shaft are bonded together to form a single
unitary structure; said spacers circumferentially spaced
symmetrically around said center shaft; said first coupling element
having an axially elongated protrusion or groove, and said second
coupling element having the other of a protrusion or a groove
configured to mate with said first coupling element; said stacked
annular laminations shrink fit to and in direct contact with said
spacers, wherein said stacked annular laminations are configured
such that an inward radial compression force is applied against
said spacers; a plurality of segmented magnets attached to an outer
surface of said stacked annular laminations; and said plurality of
segmented magnets secured to said outer surface of said stacked
annular laminations by a band wrapped circumferentially around said
segmented magnets.
26. A method of fabricating a rotor assembly of an electric motor
comprising the steps of: providing a center shaft having a first
end and an opposing second end, said center shaft configured to
rotate about a longitudinal axis; fixedly attaching a plurality of
spacers to said center shaft along axially extending proximal edges
of said plurality of spacers, such that said spacers extend
radially outward from said center shaft; providing an axially
extending distal edge of at least one of said spacers with an
axially extending first coupling element; providing a plurality of
annular laminations; providing each of said annular laminations
with a second coupling element formed within an inner
circumferential surface of said annular lamination; providing a
first axial restraining element on said axially extending distal
edge of said spacers and proximate said first end of said center
shaft, providing said first axial restraining element extending in
an outward radial direction beyond an inner circumferential surface
of said plurality of annular laminations, placing a first annular
end plate over said spacers, aligning said first annular end plate
coaxially with said center shaft; heating said annular laminations;
after said placing of said first annular end plate, axially
stacking said heated annular laminations over said spacers such
that said annular laminations are coaxially aligned with said
center shaft; engaging said first coupling element of said spacer
with said second coupling element of said annular laminations such
that rotational movement of said stacked annular laminations about
said longitudinal axis relative to said center shaft is restrained;
after said stacking of said annular laminations, placing a second
annular end plate over said spacers; after said placing of said
second annular end plate, axially compressing said stacked annular
laminations between said first annular end plate and said second
annular end plate, such that an axial compression force is applied
to said stacked annular laminations; providing a second axial
restraining element extending in an outward radial direction beyond
said inner circumferential surface of said stacked annular
laminations; and engaging said second axial restraining element
with said second annular end plate such that said axial compression
force applied to said stacked annular laminations is
maintained.
27. The method of fabricating a rotor assembly of an electric motor
of claim 26, further comprising the step of forging said plurality
of spacers together with said center shaft to provide a single
unitary structure.
28. The method of fabricating a rotor assembly of an electric motor
of claim 26, further comprising the step of spacing said plurality
of spacers circumferentially and symmetrically around said center
shaft.
29. The method of fabricating a rotor assembly of an electric motor
of claim 26, further comprising the steps of: providing a plurality
of axially extending segmented magnets; attaching said segmented
magnets to an outer surface of said stacked annular laminations;
circumferentially wrapping said plurality of segmented magnets with
an outer flexible band; curing said rotor assembly such that said
outer flexible band fixedly secures said segmented magnets to said
stacked annular laminations.
Description
TECHNICAL FIELD
[0001] This disclosure relates to electric motors, and particularly
to a rotor assembly for a rotary electric magnetic motor.
BACKGROUND ART
[0002] There are various geometries for magnetic electric motors.
One geometry is the linear magnetic motor. In a linear magnetic
motor, a shaft is driven to move linearly (that is, as a straight
line translation) with respect to a stator. Another geometry is a
rotary magnetic motor. In a rotary magnetic motor, a rotor is
driven to rotate relative to a stator.
[0003] Conventional rotary electric magnetic motors generally
include a stator assembly and a rotor that is driven to rotate with
respect to the stator assembly. Typically, the rotor is at least
partially surrounded by the stator and the rotor generates a
magnetic field by virtue of having a series of built in permanent
magnets. The stator generates magnetic fields through a series of
coils or windings. By timing the flow of current in the coils with
respect to the position and/or momentum of the rotor, the
interaction of magnetic forces from the rotor and from the stator
will rotate the rotor.
[0004] Thus, in magnetic motors, magnetic fields are formed in both
the rotor and the stator. The product between these two fields
gives rise to a force, and thus a torque on the motor rotor or
shaft. The rotor thereby moves through the field of the stator due
to magnetic forces generated by energized coils in the stator.
Thus, a conventional electric motor includes a generally
cylindrical outer stator core, stator coils wound within the stator
core, and an inner rotor having permanent magnets and that moves
relative to the stator core so as to provide motion by means of
interaction with the magnetic field of the stator.
[0005] The stator conventionally includes at least one coil wound
in at least one stator core. The purpose of the stator coils is to
generate magnetic flux that interacts with permanent magnets on the
rotor. Various stator assembly configurations are known. The stator
may be built by stacking module parts, or may be formed from
radially-extending laminates, as well as by other methods. The
stator core is typically made up of many thin metal sheets, called
laminations. Laminations are used to reduce energy losses that
would result if a solid core were used.
SUMMARY
[0006] With parenthetical reference to the corresponding parts,
portions or surfaces of the disclosed embodiment, merely for the
purposes of illustration and not by way of limitation, a rotor
assembly (15) of an electric motor is provided comprising a center
shaft (16) configured to rotate about a longitudinal axis (x-x).
Extending radially outward from the center shaft are a plurality of
spacers (20a-20f). Each of the plurality of spacers are fixedly
attached to the center shaft along an axially extending proximal
edge (21) of the spacer. An axially extending distal edge (22) of
at least one of the plurality of spacers has an axially extending
first coupling element (23). A plurality of axially stacked annular
laminations (31) are coaxially aligned with the center shaft and
are radially supported by the plurality of spacers. Thus, a
plurality of voids (26) are created and defined between two
spacers, the center shaft, and the lamination stack. Each of the
plurality of stacked annular laminations has a second coupling
element (32) formed within an inner circumferential surface (33) of
each individual lamination (30). The first coupling element of the
spacer is configured to mechanically engage the second coupling
element of the stacked annular laminations, wherein rotational
movement of the plurality of stacked annular laminations about the
longitudinal axis (x-x), relative to the center shaft, is
restrained.
[0007] The plurality of spacers may comprise axially elongated
radial spokes welded to the center shaft, and the plurality of
spacers may form a single unitary structure with the center shaft.
The spacers may be circumferentially spaced symmetrically around
the center shaft.
[0008] The first coupling element may comprise an axially elongated
protrusion or groove, while the second coupling element may
comprise the other of a protrusion or a groove configured to mate
with the first coupling element. The distal edge of at least two of
the plurality of spacers may each have axially extending first
coupling portions, and each of the plurality of stacked annular
laminations may have a plurality of second coupling portions
configured to engage with the at least two first coupling
portions.
[0009] The disclosed stacked annular laminations may be in direct
contact with the spacers, and may be shrink fit to the spacers. The
stacked annular laminations may be configured such that an inward
radial compression force (61) is applied against the spacers. Each
of the stacked annular laminations may be joined together by this
inward radial compression force, such that an external bonding
agent is not used or needed to join together each of the individual
annular laminations of the lamination stack.
[0010] Each of the plurality of spacers may have on the distal
axial edge and at a first end (38) of the stacked annular
laminations, a first axial restraining element (40) extending in an
outward radial direction beyond the inner circumferential surface
of the plurality of stacked annular laminations. A first annular
end plate (41) may be coaxially aligned with the center shaft and
positioned axially between a first end annular lamination of the
stacked annular laminations and the first axial restraining
element. Each of the plurality of spacers may further have, on the
distal axial edge and at a second opposing end (39) of the stacked
annular laminations, a second axial restraining element (42)
extending in an outward radial direction beyond the inner
circumferential surface of the stacked annular laminations. A
second annular end plate (43) may be coaxially aligned with the
center shaft and positioned axially between a second end annular
lamination of the stacked annular laminations and the second axial
restraining element, and the plurality of stacked annular
laminations may then be compressed between the first annular end
plate and the second annular end plate, such that an axial
compression force (60) is applied to the plurality of stacked
laminations. Each annular end plate may contain a plurality of
mounting holes (48) for optionally attaching one or more balancing
weights (46).
[0011] The first axial restraining element may comprise a
transversely extending recess (24) having a recess entrance (25) on
the distal edge of at least one of the spacers and a restraining
key (50) partially supported in the recess and extending in an
outward radial direction beyond the recess entrance and the inner
circumferential surface of the stacked annular laminations. The
restraining key may have a length and a thickness that varies with
the length such that the axial compression force of the plurality
of stacked laminations can be selectively varied as a function of
the length of the restraining key supported in the recess. The
second axial restraining element may comprise a restraining tab
extending from at least one of the spacers in an outward radial
direction beyond the inner circumferential surface of the stacked
annular laminations.
[0012] The rotor assembly may further comprise a plurality of
segmented magnets (54) attached to an outer circumferential surface
(37) of the stacked annular laminations. The plurality of segmented
magnets may be glued to the outer surface of the plurality of
stacked annular laminations, and may be further secured to the
plurality of stacked annular laminations by an outer band (55)
wrapped circumferentially around the segmented magnets. Each
individual annular lamination may have a series of alternating
protrusions (34), forming slots (36) around the outer
circumferential surface (37) of the annular lamination, such that
when the plurality of annular laminations are stacked over the
spacers, the plurality of lamination protrusions and slots line up
to form a plurality of magnet channels, within which each segmented
magnet will be fixedly attached.
[0013] In another aspect, a rotor assembly of an electric motor is
provided comprising a center shaft configured to rotate about a
longitudinal axis and a plurality of spacers extending radially
outward from the center shaft. Each of the plurality of spacers is
fixedly attached to the center shaft along an axially extending
proximal edge of the spacer. A plurality of axially stacked annular
laminations are coaxially aligned with the center shaft and
radially supported on an inner circumferential surface by the
plurality of spacers. Each of the plurality of spacers has, at a
first axial end of the stacked annular laminations, a first axial
restraining element extending in an outward radial direction beyond
the inner circumferential surface of the plurality of stacked
annular laminations. Further, each of the plurality of spacers has,
at a second axial end of the stacked annular laminations, a second
axial restraining element extending in an outward radial direction
beyond the inner circumferential surface of the stacked annular
laminations, and the plurality of stacked annular laminations are
compressed between the first axial restraining element and the
second axial restraining element, such that an axial compression
force is applied to the plurality of stacked laminations.
[0014] The rotor assembly may further comprise a first annular end
plate coaxially aligned with the center shaft and positioned
axially between a first end annular lamination of the stacked
annular laminations and the first axial restraining element, and a
second annular end plate coaxially aligned with the center shaft
and positioned axially between a second end annular lamination of
the stacked annular laminations and the second axial restraining
element. The plurality of stacked annular laminations may be
compressed between the first annular end plate and the second
annular end plate, such that an axial compression force is applied
to the plurality of stacked laminations. Each of the stacked
annular laminations may be joined together by the axial compression
force, such that an external bonding agent is not used to join
together each of the stacked annular laminations.
[0015] The first axial restraining element may comprise a
transversely extending recess having a recess entrance in the
distal edge of at least one of the spacers, and a restraining key
partially supported in the recess and extending in an outward
radial direction beyond the recess entrance and the inner
circumferential surface of the stacked annular laminations. The
restraining key may have a length and a thickness that varies with
the length such that the axial compression force of the plurality
of stacked laminations can be selectively varied as a function of
the length of the restraining key extending into the recess. The
second axial restraining element may comprise a restraining tab
extending from at least one of the spacers in an outward radial
direction beyond the inner circumferential surface of the stacked
annular laminations.
[0016] The distal edge of at least one of the plurality of spacers
may have an axially extending first coupling element, and each of
the plurality of stacked annular laminations may have a second
coupling element formed within the inner circumferential surface of
the lamination. The first coupling element of the spacer may be
configured to mechanically engage the second coupling element of
the stacked annular laminations, wherein rotational movement of the
plurality of stacked annual laminations about the longitudinal axis
relative to the center shaft is restrained.
[0017] The spacers may be welded to the center shaft such that the
spacers and the center shaft are bonded together to form a single
unitary structure, and the spacers may be circumferentially spaced
symmetrically around the center shaft.
[0018] The first coupling element may have an axially elongated
protrusion or groove, with the second coupling element having the
other of a protrusion or a groove configured to mate with the first
coupling element.
[0019] The stacked annular laminations may be shrink fit to and in
direct contact with the spacers, wherein the stacked annular
laminations are configured such that an inward radial compression
force is applied against the spacers. A plurality of segmented
magnets may be fixedly attached to an outer surface of the stacked
annular laminations, and the plurality of segmented magnets may be
further secured to the outer surface of the stacked annular
laminations by an outer band wrapped circumferentially around the
segmented magnets.
[0020] In another aspect a method of fabricating a rotor assembly
of an electric motor is provided. A center shaft having a first end
and an opposing second end is provided, the center shaft configured
to rotate about a longitudinal axis. A plurality of spacers are
fixedly attached to the center shaft along axially extending
proximal edges of the plurality of spacers, such that the spacers
extend radially outward from the center shaft. An axially extending
distal edge of at least one of the spacers is provided with an
axially extending first coupling element. A plurality of annular
laminations are provided, each of the annular laminations further
provided with a second coupling element formed within an inner
cylindrical surface of the annular lamination. A first axial
restraining element is provided on the axially extending distal
edge of the spacers and proximate the first end of the center
shaft. The first axial restraining element is provided extending in
an outward radial direction beyond an inner circumferential surface
of the plurality of annular laminations. A first annular end plate
is placed over the spacers, the first annular end plate aligned
coaxially with the center shaft. The annular laminations are
heated, and then, after the placing of the first annular end plate,
the heated annular laminations are axially stacked over the spacers
such that the annular laminations are coaxially aligned with the
center shaft. The first coupling element of the spacer is engaged
with the second coupling element of the annular laminations such
that rotational movement of the stacked annular laminations about
the longitudinal axis relative to the center shaft is restrained.
After the stacking of the heated annular laminations, a second
annular end plate is placed over the spacers. After the placing of
the second annular end plate, the stacked annular laminations are
axially compressed between the first annular end plate and the
second annular end plate, such that an axial compression force is
applied to the stacked annular laminations. A second axial
restraining element is provided, extending in an outward radial
direction beyond the inner circumferential surface of the stacked
annular laminations, and the second axial restraining element is
engaged with the second annular end plate such that the axial
compression force applied to the stacked annular laminations is
maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view showing a rotor assembly of an
electric motor according to a first embodiment.
[0022] FIG. 2 is an exploded view of the rotor assembly of FIG.
1.
[0023] FIG. 3 is a perspective view of the center shaft with
plurality of spacers of FIG. 1.
[0024] FIG. 4 is an elevation view of an annular lamination of FIG.
1.
[0025] FIG. 5 is a perspective view of the annular lamination of
FIG. 4.
[0026] FIG. 6 is a transverse cross sectional view of the rotor
assembly of FIG. 1, taken from the middle of the center shaft.
[0027] FIG. 7 is a perspective view of a plurality of stacked
annular laminations and end plates engaged with a center shaft and
a plurality of spacers of FIG. 1.
[0028] FIG. 8 is an enlarged fragmentary view showing an axial
restraining element of FIG. 1.
[0029] FIG. 9 is an enlarged fragmentary view showing an
alternative axial restraining element of FIG. 1.
[0030] FIG. 10 is an axial cross sectional view of the rotor
assembly, taken through the center shaft and a plurality of
spacers, in an uncompressed lamination stack configuration.
[0031] FIG. 11 is an axial cross sectional view of a rotor assembly
of FIG. 10 in a compressed and restrained lamination stack
configuration.
[0032] FIG. 12 is an axial cross sectional view of FIG. 11, and
further showing a plurality of segmented magnets and an outer
band.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] At the outset, it should be clearly understood that like
reference numerals are intended to identify the same structural
elements, portions or surfaces consistently throughout the several
drawing figures, as such elements, portions or surfaces may be
further described or explained by the entire written specification,
of which this detailed description is an integral part. Unless
otherwise indicated, the drawings are intended to be read together
with the specification, and are to be considered a portion of the
entire written description of this invention. As used in the
following description, the terms "horizontal", "vertical", "left",
"right", "up" and "down", as well as adjectival and adverbial
derivatives thereof (e.g., "horizontally", "rightwardly",
"upwardly", etc.), simply refer to the orientation of the
illustrated structure as the particular drawing figure faces the
reader. Similarly, the terms "inwardly" and "outwardly" generally
refer to the orientation of a surface relative to its axis of
elongation, or axis of rotation, as appropriate.
[0034] The instant disclosure is directed to a rotor design that
reduces material requirements, rotor weight and operational inertia
as compared with previous rotor designs, while maintaining required
structural integrity. Referring now to the drawings, and more
particularly to FIG. 1 thereof, an improved rotor assembly is
provided, of which a first embodiment is generally indicated at 15.
As will be described below, rotor assembly 15 generally comprises a
center shaft 16 oriented about longitudinal axis x-x, a plurality
of radially-extending spacers in the form of ribs or spokes
20a-20f, a laminated cylindrical back iron rotor stack 31 supported
by spacers 20a-20f and coaxially aligned with center shaft 16, and
annular end plates 41, 43 having the same inner diameter as the
inner diameter of laminated stack 31 and also coaxially aligned
with center shaft 16.
[0035] FIG. 1 illustrates rotor assembly 15 fully assembled. Rotor
assembly 15 includes a center shaft 16 having a first end 18 and an
opposing second end 19, and center shaft 16 is configured to rotate
about a longitudinal axis x-x. Fixedly attached to center shaft 16
are plurality of spacers 20a-20f, which extend radially outward
from center shaft 16. Outer band 55 surrounds the exterior
circumferential surface of laminated stack 31 of rotor assembly 15,
which is disposed axially between a first annular end plate 41 and
a second annular end plate 43.
[0036] As illustrated in FIG. 1, first annular end plate 41 is
restrained in the axial x-x direction between lamination stack 31
and first axial restraining elements 40a-40f of spacers 20a-20f,
respectively. First axial restraining elements 40a-40f extend from
a distal axial edge of each spacer 20a-20f, proximate to first end
18 of center shaft 16, in an outward radial direction beyond an
inner circumferential surface of first annular end plate 41, such
that first annular end plate 41 is restrained from moving any
farther in the x-x direction towards first end 18. It can be
appreciated that second annular end plate 43 is also constrained by
corresponding second axial restraining elements 42a-42f (not
shown), as is discussed below in further detail.
[0037] First and second annular end plates 41, 43 serve a number of
purposes, as is further discussed below, including helping to
balance rotor assembly 15 during operation. First and second
annular end plates 41, 43 preferably comprise a plurality of
mounting holes 48, to which one or more optional balancing weights
46 may be attached. The use of any such combination of balancing
weight 46 and mounting holes 48 may depend on calibration testing
performed on a fully assembled rotor 15.
[0038] Turning to FIG. 2, illustrated is an exploded view of rotor
assembly 15. Center shaft 16 and spacers 20a-20f are preferably
fixedly attached to each other, forming a single, unitary
structure. FIG. 2 further shows first and second annular end plates
41, 43, in addition to outer band 55, as described with reference
to FIG. 1. The exploded nature of FIG. 2 also reveals lamination
stack 31, segmented magnets 54, and restraining keys, severally
indicated at 50, which were not visible in FIG. 1.
[0039] Lamination stack 31 is comprised of a plurality of
individual thin annular laminations (see FIG. 4), axially stacked
and coaxially aligned with center shaft 16, and radially supported
by spacers 20a-20f. A plurality of segmented magnets, severally
indicated at 54, are attached to an outer circumferential surface
of lamination stack 31. Segmented magnets 54 are preferably glued
to lamination stack 31, and are further secured in place by outer
band 55. Restraining keys 50 comprise a portion of second axial
restraining element 42 (not shown), as is discussed below in
further detail.
[0040] FIG. 3 illustrates a perspective view of center shaft 16 and
plurality of spacers 20a-20f. Shaft 16 is preferably a solid
cylindrical member orientated about central longitudinal axis x-x.
Each spacer 20a-20f is welded using submerged arc welding directly
to center shaft 16 along axially extending proximal edge 21
extending substantially along axis x-x. As illustrated, six spacers
20a-20f, in the form of ribs or spokes, are circumferentially
spaced symmetrically around center shaft 16 and extend radially
from center shaft 16. Each spacer 20a-20f extends radially outward
away from center shaft 16 to distal edge 22, also extending
substantially along axis x-x.
[0041] Spacers 20a-20f are sized, shaped, and positioned to
minimize inertia but distribute stresses evenly. While ribs are
shown, spacers 20a-20f can take on various shapes and sizes, such
as rectangular, trapezoidal, curved, etc. depending on the
requirements of the particular rotor. It is desired that rotor
assembly be designed with a minimal number of ribs having the
smallest size that can withstand the highest required torque
transmission, both for low cycle fatigue and high cycle fatigue,
and be shaped such that inertia can be minimized and stress and be
evenly distributed.
[0042] Spacers 20b and 20e have, adjacent to distal edge 22, a
first coupling element 23. In this embodiment, first coupling
element 23 comprises protrusions 23b and 23e extending radially
from the distal ends of spacers 20b and 20e. Protrusions 23b, 23e
are configured to mate with a corresponding second coupling element
32 in each annular lamination 30 (not shown), which in this
embodiment comprises a slot. While coupling elements 23b and 23e
are shown to be axially extending protrusions and coupling elements
32b and 32e are corresponding slots or grooves, it is appreciated
that any number or type of coupling mechanism or combinations of
elements can be used to mechanically engage spacers 20a-20f with
each annular lamination 30. Spacers 20a-20f are each shown with
first axial restraining element 40a-40f, respectively, on axially
extending distal edge 22a-22f and proximate first end 18 of center
shaft 16.
[0043] As further described below, axially extending distal edges
22b and 22e of at least two opposed spacers 20b and 20e include
axially-extending keys or protrusions 23b, 23e that are configured
to be received in a corresponding axially-extending inwardly-facing
radially-open key slot or groove 32b, 32e formed in inner
circumferential surface 33 of laminated stack 31.
[0044] FIG. 3 shows spacers 20a-20f as having, on distal edges
22a-22f and proximate second end 19 of center shaft 16, a
transversely extending recess 24a-24f having a recess entrance
25a-25f, respectively. Each recess 24a-24f combines with a
corresponding restraining key 50 (as shown in FIG. 2) to form
second axial restraining elements 42a-42f (not shown), as is
discussed below in further detail.
[0045] Turning to FIGS. 4 and 5, illustrated are views of an
individual annular lamination 30, according to a preferred
embodiment of the disclosure. Annular lamination 30 is preferably
formed from a thin annular electrical steel laminate, about 0.55 mm
in thickness. Annular lamination 30 is generally defined by an
outer circumferential cylindrical surface 37 and an inner
circumferential cylindrical surface 33.
[0046] Within inner circumferential surface 33 is at least one
groove 32b, 32e, which is configured to mechanically receive
protrusion 23 of each of spacers 20b, 20e. Laminated stack 31 is
preferably formed from a multiplicity of stacked laminate layers or
rings 30. For example, a medium stack length of rotor 15 may be
1400 individual laminate layers 30. In a preferred embodiment, each
annular laminate layer 30 of the stack includes at least two
grooves 32b, 32e, indicated as opposed radially-open slots for
receiving respective keys 23b, 23e of the corresponding opposed
spacers 20b, 20e. Additional first and second coupling elements are
primarily provided to allow for variations machining processes,
whereby the mating of one set of the coupling elements might not be
exactly aligned.
[0047] Annular lamination 30 is further shown having, on outer
circumferential surface 37, a plurality of protrusions 34 defining
a plurality of slots 36 there between. The spacing between
protrusions 34, and as a result the size of slots 36, corresponds
to the width of segmented magnets 54 (not shown), such that
segmented magnets 54 fit snugly within longitudinally or axially
extending channels formed when a plurality of annular laminations
30 are axially stacked together over spacers 20a-20f, as is further
discussed below.
[0048] FIG. 6 is a transverse cross sectional view of rotor
assembly 15, taken from the middle of center shaft 16. In a
preferred embodiment, a plurality of annular laminations 30 are
heated, then axially stacked directly over spacers 20a-20f, such
that annular laminations 30 are coaxially aligned with center shaft
16 and are radially supported by plurality of spacers 20a-20f.
Protrusions 23b, 23e of spacers 20b, 20e as received in
corresponding grooves 32b, 32e of each annular lamination 30,
wherein rotational movement of each annular lamination about
longitudinal axis x-x (see FIG. 7) relative to center shaft 16 is
restrained by protrusions 23b, 23e in grooves 32b, 32e of stack
31.
[0049] FIG. 6 further illustrates that plurality of spacers 20a-20f
are preferably axially elongated radial spokes welded directly to
center shaft 16, and that annular laminations 30 contact spacers
20a-20f directly, without any intervening shroud or sleeve disposed
in between. Spacers 20a-20f are preferably circumferentially spaced
symmetrically around center shaft 16, such that voids, severally
indicated at 26, are defined within the spaced demarcated by two
adjacent spacers, such as spacers 20a and 20b, center shaft 16, and
inner circumferential surface 33 of annular laminations 30.
[0050] FIG. 6 additionally illustrates a plurality of segmented
magnets 54 disposed circumferentially around outer surface 37 of
annular lamination 30 within each magnet slot 36 defined between
each lamination protrusion 34. Segmented magnets 54 are preferably
glued to channels formed by stacked magnet slots 36 on outer
circumferential surface 37 of annular lamination 30, and segmented
magnets are further secured to outer circumferential surface 37 of
annular lamination 30 by outer band 55. While axially extending
segmented magnets are preferred, it is appreciated that other types
of magnets, such as annular magnets, can be used.
[0051] Outer band 55 is preferably a fiberglass band, which is
applied over magnets 54 and then cured, which helps to avoid
magnets 54 flying off during the operation of rotor assembly 15 due
to poor bonding of segmented magnets 54 to laminated stack 31.
While fiberglass is a preferred material, any other type of strong,
flexible, non-magnetic material can be used.
[0052] As illustrated in FIG. 7 and discussed with reference to
FIG. 6 above, plurality of annular laminations 30 are axially
stacked over spacers 20a-20f, thus forming annular lamination stack
31. Stack 31 appears in FIG. 7 to have a smooth, continuous outer
surface due to the extreme thinness (approximately 0.55 mm) of each
individual laminate 30. Annular lamination stack 31 is coaxially
aligned with center shaft 16 and is radially supported by plurality
of spacers 20a-20f. In a preferred embodiment, since each annular
lamination 30 is heated prior to forming stack 31, annular
lamination stack 31 is shrink fit to spacers 20a-20f, such that
annular lamination stack 31 exerts an inward radial compression
force along arrows 61. Further, annular lamination stack 31 is
preferably compressed axially in the x-x direction between first
and second annular end plates 41, 43, with annular end plates 41,
43 being constrained in the axial x-x direction by tabs 40a-40f and
recesses/keys 42a-42f (not shown).
[0053] A small clearance is provided between keys 23b, 23e of
respective spacers 20b, 20e and key slots 32a, 32e of laminated
stack 31, and an interference fit is formed between inner diameter
33 of laminated stack 31 and distal ends 22b, 22e of spacers 20b,
20e. Thin annular laminations 30 are heated during assembly as they
are stacked around spacers 20a-20f such that when they cool stack
31 shrinks to fit directly on to rotor spacers 20a-20f. Given the
elasticity of laminations 30, a force or load is thereby applied
radially inwardly on spacers 20a-20f. There is no additional welded
metal structural ring or sleeve between laminated stack 31 and
spacers 20a-20f. Laminated stack 31 is shrink-fit directly to
spacers 20a-20f. This provides a lower mass rotor and better
magnetic permeability.
[0054] During assembly, center shaft 16 is preferably orientated
vertically with the drive end down. First end plate 41 is placed
around spacers 20a-20f and down against the upwardly facing
retaining surfaces of tab elements 40a-40f, which are preferably in
the form of rib projections or tabs, as illustrated. Thin annular
steel laminates 30 of stack 31 are heated and then dropped and
stacked on each other around spacers 20a-20f, with a bottom annular
end face of a first laminate bearing against an inner annular end
face of first end plate 41. Once stack of laminates 31 has reached
a desired height, second annular end plate 43 is placed on top and
is pressed down against stacked laminate layers 31 and first end
plate 41 and first axial restraining elements 40a-40f, to thereby
axially load laminated stack 31 to a desired stack pressure. This
stack pressure in then maintained via second axial restraining
elements 42a-42f.
[0055] FIGS. 8 and 9 illustrate enlarged fragmentary views of first
and second restraining elements 40 and 42. In FIG. 8, first annular
end plate 41 is engaged with restraining tabs 40a-f. In this
instance, first restraining elements 40a-40f take the form of
restraining tabs extending from respective distal edges 22a-22f at
a first end of each spacer 20a-20f in an outward radial direction
beyond inner circumferential surface 33 of plurality of stacked
annular laminations 31. In FIG. 9, second annular end plate 42 is
engaged with restraining recesses/keys 42a-42f. In this instance,
each second restraining element 42a-42f comprises transversely
extending recesses severally indicated at 24 within respective
distal edges 22a-22f at a second end of each spacer 20a-20f,
combined with restraining keys 50 at least partially supported
within recesses 24 and also extending in an outward radial
direction beyond inner circumferential surface 33 of lamination
stack 31. While tabs, recesses, and keys are used as restraining
elements in the instant embodiment, it is envisioned that any
suitable element(s) for similarly axially restraining annular end
plates 41 and 43 may be used.
[0056] With further reference to FIG. 9, in a preferred embodiment
of the disclosure, distal edges 22a-22f of spacers 20a-20f on
second end 19 of shaft 16 each include a transversely-extending
outwardly facing radially-open key slot or recess 24 configured to
receive transversely extending keys or restraining elements 50 that
will constrain an outer annular end face of a non-drive end of
second end plate 43. When a desired stacking pressuring has been
applied to laminated stack 31 as described above, restraining key
or element 50 is placed in transversely-extending radially-open key
slot or recess 24, with a portion extending radially beyond an
inner diameter of second end plate 43 and laminated stack 31.
Restraining key 50 is then fixedly attached into place, preferably
by welding restraining key 50 to both recess 24 and to second end
plate 43. Such restraining element 42 constrains axial movement of
laminated stack 31 in a direction toward second end 19 along
central axis x-x of shaft 16. A thickness of restraining element 50
may be adjusted to maintain the desired axial stack pressure. In
this manner, laminated stack 31 is axially compressed between end
plates 41, 43 and a compression stress on laminations 31 is thereby
provided.
[0057] A method of fabricating rotor assembly 15 of an electric
motor is now described with reference to FIGS. 10-12, which
illustrate axial cross sectional views of multiple embodiments of
rotor assembly 15, taken through the center shaft 16 and a
plurality of spacers 20b, 20e. As shown in FIG. 10, center shaft 16
is provided with a plurality of spacers 20a-20f fixedly attached to
center shaft 16, wherein center shaft 16 and spacers 20a-20f
preferably form a single integrated structure. Spacers 20a-20f
extend radially outward from center shaft 16. A plurality of
annular laminations 30 are provided. In one embodiment, axially
extending distal edges 22a-22f of at least one of spacers 20a-20f
is provided with an axially extending first coupling element 23b,
23e, and each of said annular laminations 30 are provided with
second coupling element 32b, 32e formed within inner
circumferential surface 33 of each annular lamination 30, as
described hereinabove.
[0058] First axial restraining element 40a-40f of each spacer
20a-20f is provided on axially extending distal edge 22a-22f of
each spacer 20a-20f and proximate first end 18 of center shaft 16.
First axial restraining element 40a-40f is further provided
extending in an outward radial direction beyond inner
circumferential surface 33 of each annular lamination 30. Next,
first annular end plate 41 is placed over spacers 20a-20f, such
that first annular end plate is aligned coaxially with center shaft
16.
[0059] Each annular lamination 30 is then heated. After the placing
of first annular end plate 41, the heated annular laminations 30
are axially stacked over spacers 20a-20f such that annular
lamination stack 31 is formed and is coaxially aligned with center
shaft 16. First coupling element 23b, 23e of spacer 20b, 20e is
engaged with second coupling element 32b, 32e of each annular
lamination 30 such that rotational movement of annular lamination
stack 31 about longitudinal axis x-x relative to center shaft 16 is
restrained. At this stage, annular lamination stack 31 is
uncompressed. As illustrated in FIG. 10, uncompressed lamination
stack 31 extends axially beyond recess entrance 25 of transversely
extending recess 24 of spacer 20. In one embodiment, recess 24
measures approximately 10 mm in the axial direction.
[0060] Turning to FIG. 11, after annular lamination stack 31 is
assembled over spacers 20a-20f and is in an uncompressed state,
second annular end plate 43 is then placed over spacers 20a-20f.
After the placing of second annular end plate 43, lamination stack
31 is axially compressed between first annular end plate 41 and
said second annular end plate 43, such that axial compression force
60 is applied to annular lamination stack 31.
[0061] Next is provided second axial restraining element 42a-42f,
comprising restraining keys 50 and recesses 24. Restraining keys 50
are engaged with recesses 24 and second annular end plate 43 such
that axial compression force 60 applied to stacked annular
laminations 31 is maintained. Further, because lamination stack 31
was shrink fit directly to plurality of spacers 20a-20f, lamination
stack 31 exerts an inward radial force 61 towards center shaft 16.
The combination of inward radial force 61 and axial compression
force 60 allows for the plurality of annular laminations 30 of
lamination stack 31 to be held together without the need for glue,
welding, or any other bonding agent. In one embodiment, each
restraining key 50 is manufactured after lamination stack 31 is
compressed, so that each restraining key 50 can be made to be the
exact size needed. For example, if recess 24 measures approximately
10 mm in the axial direction, and compressed lamination stack 31
extends in the axial direction 4 mm over the top of recess entrance
25 and leaving a 6 mm open gap over recess 24, then restraining key
50 can then be manufactured to have a thickness of 6 mm, so that
the open gap is completely filled and the desired compression force
of stack 31 is maintained.
[0062] Continuing the method of fabricating rotor assembly 15 of an
electric motor with reference to FIG. 12, after second axial
restraining element 42a-42f is secured, plurality of segmented
magnets 54 are preferably glued to outer circumferential surface 37
of lamination stack 31. To further secure plurality of segmented
magnets 54 to outer circumferential surface 37 of lamination stack
31, outer band 55 is applied to rotor assembly 15, covering the
entirety of an outer surface of segmented magnets 54. A surface
mounted permanent magnet rotor design with low inertia is thus
achieved. In particular, the rotor assembly reduces material
requirements, rotor weight and operational inertia, while
maintaining required structural integrity.
[0063] The present invention contemplates that many changes and
modifications may be made. Therefore, while the presently-preferred
form of the rotor has been shown and described, and several
modifications and alternatives discussed, persons skilled in this
art will readily appreciate that various additional changes and
modifications may be made without departing from the scope of the
invention, as defined and differentiated by the following
claims.
* * * * *